Original sin is a religious doctrine that divides perhaps more than any other. For some, it only makes sense – maybe not the part about the apple and the garden, but the general idea that humankind is flawed: we do what we wouldn't do, and don't do what we would do, as St Paul put it. For others, though, original sin is vile and offensive. It feeds the fear of hell, a hopelessness about progress, and leaves us pathetically dependent on God. Each side has a radically different view of what it is to be human, and William James understands exactly what's a stake.

It follows from one of the most interesting distinctions he draws in the Varieties. There are some, he explains, who take the happiness that religion gives them to be the amplest demonstration of its truth. Then, there are others who take the remedy that religion offers for the ills of the world to be the amplest reason for its necessity. James adopts the terms "once-born" to describe the happy sort, and "twice-born" for the more pessimistic.

The link between the phrase "once-born" and the positive temperament is that these individuals believe that seeing God – or finding fulfilment, or simply living well – is no more or less difficult than seeing the sun. On some days it will be cloudy. But the skies eventually clear.

The cosmos is fundamentally good, they affirm. Human individuals are, basically, kind. Your first birth, as a baby, is the only birth that's required to see the world aright. This temperament is, James explains, "organically weighted on the side of cheer and fatally forbidden to linger, as those of opposite temperament linger, over the darker aspects of the universe." James's favourite example of the once-born is Walt Whitman. "He has infected [his readers] with his own love of comrades, with his own gladness that he and they exist."

Alongside Whitman, there are some Christians who fall into this category. (Not all take original sin that seriously.) They are of a liberal sort, believing that the significance of Jesus is found in his moral teaching, which if followed would lead to a more perfect world. Popular science-writing has contributed to the increase of this kind of belief too, as it conveys the conviction that human beings can understand themselves and, thereby, fix themselves. Eastern ideas imported into the west offer something similar. Hence, meditation techniques, such as mindfulness, are sold as being scientific and empowering.

As is most self-help. James lived in the decades when modern self-help became a publishing phenomenon, and he lists various forms of it in the Varieties – the "gospel of relaxation"; the "don't worry movement"; the advocates of physical exercise. These have been steady earners for publishers ever since.

What connects liberal Christianity, scientific optimism and self-help is the belief that human beings can generate their own wellbeing. It may take effort. Jesus's moral teaching is tough: love your enemies. Self-help can be stringent too. And the underlying philosophies can be sophisticated, recognising that our higher motivations must be trained to overcome the lower. But what unites them is the belief that there is nothing, in theory, that prevents us from improving our lot. It's a matter of application. They are "mind-cures", as James calls them.

The twice-born school of thought, though, does not agree. Here, the overriding sense is that the human condition is affected by evil. No matter with what effort individuals apply themselves – no matter how aware a society becomes of itself – tragedy, failure and death are ever-present. "Life and its negation are beaten up inextricably together," James says. This is not to say that life is not worthwhile. But it is inevitably tainted by failure, and a fear of Sisyphean futility.

So if you are of this second persuasion, what do you do? One option is resignation. Hence, the Stoics taught their followers to go with the flow and be insensitive to life's pain. Differently, the Epicureans concluded that pain was best avoided, and that meant avoiding pleasures too: teach yourself to delight in a glass of water and you won't care when marauding Macedonians steal the wine.

However, others in this second group want more. Their solution is radical. One must seek to be born again – to be twice-born. It's a process of redemption, of new creation, of being saved. Help must come from without, not within. Tolstoy falls into this camp when, following his mental collapse, he gradually realises "something else in me was working too". It came, he believed, via the heart, and was a force that can be called God. John Bunyan was the same, associating his recovery with the salvation and relief he found in the blood of Christ.

So, according to the healthy-minded view, the pessimistic view is hopeless and morbid. Conversely, mind-cures seem woefully simplistic to the others. It's little surprise that the doctrine of original sin causes such antagonism. Nothing less than life itself is at stake.

James finds some truth in both schools. The mind-cures appeal to human dignity. They allow us to take responsibility for ourselves. That said, he tends to side more with the twice-born attitude, believing that the "sick soul" view of things provides a more profound description of the way the world actually is.

Do not possibilities imply impossibilities? Does not choice demand the loss of things not chosen? Excellence stands out against second best. One person's gain is often another's loss. The optimistic can sustain their sunny view only by ignoring the dusk, because night does indeed follow day. James argues that the mind-cure is a "fragile fiction", and that the twice-born attitude has much to commend it. However, that leads to a further topic, the nature of its conversion. It'll be our concern in the next blog.